DNA Replication DNA helix unwinds from histones DNA helix unwinds from histones Helicase untwists the double helix and exposes complementary strands Helicase untwists the double helix and exposes complementary strands The site of replication = replication bubble The site of replication = replication bubble Each nucleotide strand serves as a template for building a new complementary strand Each nucleotide strand serves as a template for building a new complementary strand

DNA Replication RNA primers begin DNA synthesis RNA primers begin DNA synthesis DNA polymerase III continues from the primer and adds complementary nucleotides to the template DNA polymerase III continues from the primer and adds complementary nucleotides to the template

DNA Replication Since DNA polymerase only works in one direction: Since DNA polymerase only works in one direction: A continuous leading strand is synthesized A continuous leading strand is synthesized A discontinuous lagging strand is synthesized A discontinuous lagging strand is synthesized DNA ligase splices together the short segments of the lagging strand DNA ligase splices together the short segments of the lagging strand

DNA Replication Figure 3.31

Cell Division Essential for body growth and tissue repair Essential for body growth and tissue repair Mitosis – nuclear division Mitosis – nuclear division Cytokinesis – division of the cytoplasm Cytokinesis – division of the cytoplasm

Mitosis The phases of mitosis are: The phases of mitosis are: Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase

Cytokinesis A cleavage furrow is formed in late anaphase by contractile ring A cleavage furrow is formed in late anaphase by contractile ring Cytoplasm is pinched into two parts after mitosis ends Cytoplasm is pinched into two parts after mitosis ends

Early and Late Prophase Asters are seen as chromatin condenses into chromosomes Asters are seen as chromatin condenses into chromosomes Nucleoli and nuclear membrane disappear Nucleoli and nuclear membrane disappear Centriole pairs separate and the mitotic spindle is formed Centriole pairs separate and the mitotic spindle is formed 2 microtubule types: polar and kinetichore 2 microtubule types: polar and kinetichore

Early Prophase Figure

Late Prophase Figure

Metaphase Chromosomes arrange themselves with their centromeres aligned at the middle of the cell Chromosomes arrange themselves with their centromeres aligned at the middle of the cell This arrangement of chromosomes = metaphase plate This arrangement of chromosomes = metaphase plate

Metaphase Figure

Anaphase Centromeres of the chromosomes split Centromeres of the chromosomes split Motor proteins in kinetochores pull chromosomes toward poles Motor proteins in kinetochores pull chromosomes toward poles

Anaphase Figure

Telophase and Cytokinesis New sets of chromosomes uncoil into chromatin New sets of chromosomes uncoil into chromatin New nuclear membrane is formed from the rough ER New nuclear membrane is formed from the rough ER Nucleoli reappear Nucleoli reappear Generally cytokinesis completes cell division Generally cytokinesis completes cell division

Telophase and Cytokinesis Figure

Control of Cell Division Surface-to-volume ratio of cells Surface-to-volume ratio of cells Chemical signals such as growth factors and hormones Chemical signals such as growth factors and hormones Contact inhibition Contact inhibition Cyclins and cyclin-dependent kinases (Cdks) complexes Cyclins and cyclin-dependent kinases (Cdks) complexes

Protein Synthesis DNA serves as master blueprint for protein synthesis DNA serves as master blueprint for protein synthesis Genes are segments of DNA carrying instructions for a polypeptide chain Genes are segments of DNA carrying instructions for a polypeptide chain Triplets of nucleotide bases = codon Triplets of nucleotide bases = codon Each triplet specifies coding for an amino acid Each triplet specifies coding for an amino acid

From DNA to Protein Figure 3.33 Nuclear envelope DNA Pre-mRNA mRNA Ribosome Polypeptide Translation RNA Processing Transcription

Roles of the Three Types of RNA Messenger RNA (mRNA) – carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm Messenger RNA (mRNA) – carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm Transfer RNAs (tRNAs) – bound to amino acids; base pair with the codons of mRNA at the ribosome to assemble proteins Transfer RNAs (tRNAs) – bound to amino acids; base pair with the codons of mRNA at the ribosome to assemble proteins Ribosomal RNA (rRNA) – a structural component of ribosomes Ribosomal RNA (rRNA) – a structural component of ribosomes

Transcription Creation of a copy of mRNA from DNA Creation of a copy of mRNA from DNA Transcription factor Transcription factor Loosens histones from DNA in the area to be transcribed Loosens histones from DNA in the area to be transcribed Binds to promoter, a DNA sequence specifying the start site of RNA synthesis Binds to promoter, a DNA sequence specifying the start site of RNA synthesis Mediates the binding of RNA polymerase to promoter Mediates the binding of RNA polymerase to promoter

Transcription: RNA Polymerase An enzyme that oversees the synthesis of RNA An enzyme that oversees the synthesis of RNA Unwinds the DNA double helix Unwinds the DNA double helix Adds complementary nucleotides on the DNA template Adds complementary nucleotides on the DNA template Joins these RNA nucleotides together Joins these RNA nucleotides together Stops transcription at a termination signal Stops transcription at a termination signal

Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA nucleotides RNA polymerase bound to promoter mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates RNA nucleotides mRNA synthesis is terminated RNA polymerase mRNA DNA mRNA transcript (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

Initiation of Translation mRNA attaches to the small subunit of the ribosome mRNA attaches to the small subunit of the ribosome Initiator tRNA binds to the small subunit Initiator tRNA binds to the small subunit The large ribosomal unit now binds to this complex forming a functional ribosome The large ribosomal unit now binds to this complex forming a functional ribosome

Genetic Code RNA codons code for amino acids according to a genetic code RNA codons code for amino acids according to a genetic code Figure 3.35

Information Transfer from DNA to RNA DNA triplets are transcribed into mRNA codons by RNA polymerase DNA triplets are transcribed into mRNA codons by RNA polymerase Codons base pair with tRNA anticodons at the ribosomes Codons base pair with tRNA anticodons at the ribosomes Amino acids are bonded to form polypeptide chains Amino acids are bonded to form polypeptide chains Start and stop codons are used in initiating and ending translation Start and stop codons are used in initiating and ending translation

Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Once its amino acid is released, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme

Information Transfer from DNA to RNA Figure 3.38